THURSDAY, July 27, 2017 (HealthDay News) -- A donated kidney is turned away for transplant an average of seven times before reaching the patient who finally receives it, a new study shows.

Transplant centers regularly reject kidneys based on a donor's age or perceived quality of the organ, even though these kidneys are eventually accepted and work well for people farther down the waiting list, explained lead researcher Dr. Anne Huml, a nephrologist and health disparities fellow with Case Western Reserve University in Cleveland.

The centers are likely being appropriately picky in selecting organs, to ensure the greatest chance of success by carefully matching each kidney to each recipient, Huml said.

"If someone's been waiting five years, why rush and take the first kidney offered when within a month they'll be offered a better kidney and their outcome will be better?" Huml said.

But such hesitation can mean that patients high on the waiting list remain on dialysis while organs that would have suited them fine pass down to others who've waited less time, said Dr. Sumit Mohan, an associate professor for medicine and epidemiology at Columbia University's Mailman School of Public Health.

"The general sense is that surgeons are less willing to take risks, so what ends up happening is there are a large number of kidneys that people say no to that end up getting transplanted way down the list," said Mohan, who co-authored an editorial accompanying the study. Both appear in the July 27 issue of the Clinical Journal of the American Society of Nephrology.

Worse, patients rarely are told that their transplant center has passed on a donor kidney offered to them, Mohan said.

"If your surgeon says no, I don't want that kidney, you're never informed. You're not even told that's the case," Mohan said. "Patients need to be more engaged in the process and have a better understanding of what's being agreed to on their behalf."

More than 100,000 people currently are waiting for a kidney transplant in the United States, Mohan said.

Dialysis keeps a delay in receiving a kidney from becoming immediately life-threatening, Huml said. However, there is a high mortality rate associated with dialysis, and people who are on dialysis longer don't do as well once they have received a kidney, Mohan said.

For the study, Huml and her colleagues reviewed more than 7 million organ offers that were made for 31,230 kidneys from deceased donors between 2007 and 2012. All the kidneys were eventually transplanted.

The researchers found that donor kidneys were offered a median of seven times to different patients before being accepted for transplantation.

Centers most often gave a pass to a donated kidney either based on donor-related factors such as age of the person or quality of the organ, or because the minimal acceptable criteria for a transplant center had not been met. Each of those two general reasons accounted for 3.2 million rejected offers, or around 45 percent.

Transplant centers largely pass on kidneys from donors with high blood pressure, a history of diabetes, reduced kidney function or death related to heart problems, the researchers found.

In those cases, centers that want to keep their success rates high are rejecting organs that appear dicey, even though they end up being successfully transplanted into another patient, Mohan said.

The study also found that transplant centers are more picky in choosing kidneys for patients who are male, Hispanic, overweight or obese, or suffering from high blood pressure resulting from kidney failure, Huml said.

Patients with medical problems such as excess weight or high blood pressure likely face more difficult surgeries, and so doctors are more choosy about the kidney that's right for them, Mohan explained.

"Those are much harder patients to operate on, and the risk of complications is higher," he said.

The longer waits for men and Hispanics also could be related to these medical problems, Mohan added. For example, men needing kidney transplants might be more likely to have high blood pressure or be obese than their female counterparts.

Centers are trying to maximize the effect of transplantation by steering organs to the right people, said Dr. David Klassen, chief medical officer for the United Network for Organ Sharing, the private nonprofit that manages the nation's organ transplant system.

For example, it makes little sense to transplant a very healthy kidney expected to work for 40 years into a 70-year-old person with a life expectancy of 10 years, he said.

That said, changes made to the organ allocation system in 2014 have addressed some of the concerns raised by this study, Klassen said.

The changes require that minorities receive a percentage of donated organs that reflects the percentage of waiting list patients they represent, Klassen said.

In addition, officials changed the way waiting time is calculated, Klassen said. Waiting time is now calculated from the time you were put on dialysis, to reflect the fact that dialysis is riskier for patients.

Mohan recommended two additional reforms to the system that could help get kidneys to appropriate patients more quickly:

Provide feedback to transplant centers on organs they reject that wind up being acceptable elsewhere. "I think we have an obligation to go back to the transplant center and say somebody else chose to use that kidney," he said. "You may want to rethink that clinical choice you made."

Give patients access to organ acceptance rates at transplant centers near them. "If I want to make an informed choice as a consumer, I want to know be able to look at how aggressive is a certain center, how willing are they to take certain kinds of organs, what is the wait time," Mohan said. "We need to provide that information to patients if they are going to make these choices."